Preparation And Room Temperature Catalytic HCHO Oxidation Performance Of Manganese Oxide Composite Thermal Catalysts

Formaldehyde is one of the major indoor air pollutants.Long-term exposure to formaldehyde can cause serious damage to human health.Catalytic oxidation by transition metal oxide is a practical method for formaldehyde removal.In this paper,MnO₂/PET,MnO₂/AlOOH and MnO₂/AlOOH/Al composite catalysts were prepared by reduction of KMnO₄ and applied to formaldehyde removal at room temperature.First,the MnO₂/PET composite catalyst was prepared by reducing KMnO₄ with-OH on the surface of the hydrolyzed PET fiber at room temperature.Methanol was added to increase the amount of MnO₂ produced.The synthesized MnO₂ partially wrapped on the surface of the PET fiber.The growth process of MnO₂ on PET surface was divided into in-situ surface synthesis and surface deposition.In static tests,MnO₂/PET exhibited good ability to remove formaldehyde at room temperature.The catalytic behavior appeared as an"adsorption-oxidation"process.The preparation of MnO₂/PET composite catalyst at room temperature confirms the feasibility of this MnO₂ synthesis method.The AlOOH powder,which has an ultra-high specific surface area and a large amount of surface-OH,was prepared by a simplified microemulsion method.Different proportions of MnO₂/AlOOH composite catalysts were further prepared by reaction of AlOOH with KMnO₄.The composite had a higher ability to remove indoor formaldehyde compared to the birnessite MnO₂ at room temperature and A₁₀M₆ showed the best performance.MnO₂ was uniformly distributed in AlOOH and exhibits a partially crystalline structure,containing multivalent Mn ions and a large number of defects which facilitate charge exchange.Through the charge exchange of Al ions,Mn ions and vacancy defects,the nearby-OH could have strong oxidizing activity and became active site for formaldehyde oxidation.The presence of Al ions facilitated charge exchange on the one hand,and on the other hand favored the formation of partial crystalline structures that influence the valence state of Mn ions to produce oxidizing high-valence Mn ions.Combined with the characterization and performance tests of MnO₂,MnO₂/PET and MnO₂/AlOOH composite catalysts,the reaction mechanism for the removal of low concentrations formaldehyde at room temperature by transition metal oxide catalysts was summarized and described as adsorption,oxidation and self-regeneration.Unlike most studies that focus on improving the performance of MnO₂,this is a new type of composite catalyst obtained through MnO₂ modification and played synergy.In order to immobilize the MnO₂/AlOOH composite catalyst,combining the hydrothermal reaction to grow AlOOH on the surface of Al wire,the MnO₂/AlOOH/Al composite catalyst was prepared by two-step reaction.The hydrothermal reaction at120°C succeeded in synthesising willow-like AlOOH nanosheets on the surface of Al wire.However,MnO₂ was difficult to generate by immersing the AlOOH/Al sample in KMnO₄ solution at room temperature.The addition of NaOH slightly increased the amount of MnO₂ produced.Furthermore,the MnO₂/AlOOH complex was directly formed on the surface of Al wire by a one-step hydrothermal reaction,in which the amount of surface oxides was significantly improved.The effects of different amounts of NaOH added on the products were compared.Besides the AlOOH,the oxides formed on the Al wire also included MnO₂/AlOOH composites,δ-MnO₂ and amorphous MnO₂.In contrast,MAA-2T with a variety of MnO₂ species had good formaldehyde removal performance.